In the Wireless Relay technology in the Advanced long term evolution (LTE-Advanced) standard released by the 3GPP standard organization, the Relay Node (RN) provides the function and service similar to those provided by the common evolved NodeB (eNB) to the UE accessing to its cell, and accesses in a way similar to the common UE a donor Node Bdonor (DeNB) which serves it through the air interface. As the high-speed railway is built and put into operation on a large scale, the demand for communicating on the train is increasing constantly. But because the high-speed moving train is influenced by the Doppler shift, the frequent cell handover and the large penetration loss of the high-speed rail carriage, etc., the coverage of the existing network NodeB is very difficult to meet the communication quality demand of the high-speed train. So the industry proposes deploying the relay node on the high-speed train, and this kind of relay node is usually called the Mobile Relay Node (MRN). As shown in FIG. 1, through the mobile relay technology, it can make the users (UE1 and UE2) in the high-speed train perform the communication with the relatively rest MRN, and the MRN can be handed over among different DeNBs in the process of moving with the high-speed train, thus avoiding the simultaneous handover of a large number of users in the carriage of the high-speed train and guaranteeing the communication quality between the UE and the MRN; in addition, through enhancing the backbone connection between the mobile RN and the DeNB, it can better solve a series of problems existed in the high-speed rail.
If the MRN adopts the framework as shown in FIG. 1 (that is, the framework same with the already standardized R10 fix relay, usually called the framework 2), to reduce the delay of the UE data, it can consider the routing optimization scheme. When the MRN moves farther from the initial DeNB, the gateway (GW) of the MRN is handed over to the built-in gateway of the DeNB which serves the MRN. As shown in FIG. 2, before the MRN is handed over, its GW is located on the DeNB1, and the MRN is provided with the NodeB function service by the DeNB3; the data of the UE reaches the GW function of the DeNB1 at first, and then is routed to the NodeB function of the DeNB3 through the DeNB2, and the MRN can reposition its GW to the built-in GW of the DeNB4 in the handover process, thus making the data of the UE reach the DeNB4 directly, shortening the path length, and reducing the data delay.
In addition, in order to better meet the user demand and further promote the user experience, the 3GPP considers that the MRN supports the local IP access (LIPA) function to provide the high-speed local service for the LTE UE and save the bandwidth resources of the backhaul link of the air interface. For example, the UE can connect the local packet data network (PDN) through a co-located local gateway (is abbreviated as LGW) in the MRN to obtain the multimedia resources, or support the multi-user social network application, such as file-sharing, chat, game, etc., through the local server. FIG. 1 is a framework diagram that the MRN supports the LIPA function in the high-speed train scene. As shown in FIG. 1, the LGW function entity is co-located in the MRN node in the carriage, and the data are received and sent through a Un air interface between the MRN and the DeNB. The LGW is connected with the PDN network through the SGi interface. For the UE in the connection status that the LIPA connection exists, there is a direct tunnel used for the LIPA service data between the LGW and the MRN, and the LGW in the MRN establishes the S5 interface core network tunnel through the DeNB and the UE service gateway (SGW), used for the paging of the UE in the IDLE status and the S5 signaling transmission.
In the scene of the home NodeB (HeNB) supporting the LIPA, the address of the LGW co-located in the HeNB is assigned by the security gateway (SeGW) during the IPSec tunnel establishment process. But in the situation of the MRN supporting the LIPA, the MRN is not connected to the SeGW network element. And in the situation that the LGW and the MRN are not co-located, all data sent by the network element of the core network to the LGW must be routed through the gateway of the MRN packet data network (PGW), and then they could arrive. So, in the situation of the MRN supporting the LIPA, if the MRN PGW is repositioned during the handover process of the MRN, the S5 data associated to the LIPA service sent from the UE SGW cannot arrive at the MRN PGW smoothly to be routed to the LGW, which causes the S5 connection disconnect.